In the realm of body exercise and strength training, there is a need to strengthen the muscles of the thigh which are used to extend the leg at the knee. In order to build strength in the leg extension muscles, it is essential to increase the resistive load on the muscles as the user's strength level increases. It is also desirable to reduce the risk of injury and to increase range of motion as the exercise is performed.
Various exercise devices have been devised to exercise the thigh muscles as the legs are extended at the knee. These devices function by allowing the user, while seated, to rest the shins or ankles behind a weighted bar and then to force the bar forward in an upward arc as the legs are extended. Some of these devices cause the effective resistance to maximize as the knee reaches full extension when it is most vulnerable to injury. Other leg extension exercisers work on similar principles but with complicated lever arrangements without satisfactorily reducing the resistance on the leg as the leg is extended at the knee.